Hydraulic fracturing is an important step in producing oil and gas from hydrocarbon reservoirs. Traditional fracturing uses water-based fluids at high pressures to create fractures in the reservoir. Viscous fluids, such as crosslinked gels, are then pumped into the fractures carrying a suspension of proppants. The proppants serve to prevent the fractures from re-closing due to the pressure of the earth, in other words, the proppants keep the fractures open. Proppants are solid particles, such as sand or ceramics, that easily fit into the fractures. Traditional proppants have a compressive strength in the range of 1,000 to 15,000 psi. Keeping the fractures open is important as the fractures provide the conductive path through which the oil and gas can flow from the reservoir to the wellbore and the surface. After the viscous fluids carry the proppants into the fracture, the viscous fluids are allowed to flow back into the wellbore leaving the proppants behind.
Traditional fracturing fluids, including the viscous proppant laden fluids have a number of disadvantages. First, traditional fracturing with traditional proppants requires multiple injections (multi-injections), which increases the time required to fracture and place proppant. Multi-injections can also increase the chances for error, expenses, and problems to be introduced. Second, the viscous fluids can deposit solid residues from the crosslinked gels along the fractures, formation walls, or proppant packs. The deposits of solid residue can restrict the flow of oil and gas from the reservoir. Third, the proppant itself may agglomerate or pack together presenting an obstacle in a fracture through which the oil or gas is prevented from passing. Further, placement of the proppant in the fractures can be more of an art than a science, in such that the proppant may not be placed in the fracture as desired or may be screened out during the fracturing process. Finally, the proppant can experience embedment in the formation. Other concerns relate to the growing public anxieties related to the potential environmental impact of traditional hydraulic fracturing fluids, both to the significant amount of water used and from the concerns of contamination of the water table.
A method that provides for a one-step injection to fracture a reservoir and keep the fractures open without the disadvantages of traditional proppants is desired.